Exodus 32:24-28

So I said to them, ‘Whoever has any gold, let them tear it off.’ Then they gave it to me, and I threw it into the fire, and out came this calf.”

Now when Moses saw that the people were out of control—for Aaron had let them get out of control to the point of being an object of ridicule among their enemies—

Moses then stood at the gate of the camp, and said, “Whoever is for the Lord, come to me!” And all the sons of Levi gathered together to him.

And he said to them, “This is what the Lord, the God of Israel says: ‘Every man of you put his sword on his thigh, and go back and forth from gate to gate in the camp, and kill every man his brother, and every man his friend, and every man his neighbor.’ ”

So the sons of Levi did as Moses instructed, and about three thousand men of the people fell that day.